1. Field of the Invention
This invention relates to magnetic bubble domains, and more particularly, to gapless propagation structures for implementing the controlled movement of magnetic bubble domains in a supporting medium.
2. Description of the Prior Art
In the new and rapidly developing field of technology relating to magnetic bubble domains, the preferred means for implementing the controlled movement of bubbles within a supporting magnetic medium, such as orthoferrite or garnet material, has involved the use of overlay strips of permalloy or the like. These strips are magnetically soft, are adjacent to the medium, and serve to channel and concentrate the flux from a rotating in-plane magnetic field. This concentration produces poles at the ends of the strips when aligned with the rotating field, and these poles attract (or repel) the bubbles to thereby control their movement.
The permalloy structures currently in use include the T-I bar, Y-I bar, Y-Y bar and chevron patterns, and rely on gaps between the bars to provide a continuous flow of bubbles around the structures in the presence of a rotating or pulse-sequenced magnetic field.
These gapped permalloy patterns are characterized by a number of major disadvantages. For instance, the bubble shape is dramatically distorted at the gaps which reduces the operating margins. Further, a bubble typically comes to a stop at the gaps which reduces the average propagation velocity and thus the data rate. In addition, a bubble must be elevated to a high energy state to traverse the gap, which renders it momentarily less stable and thus more likely to collapse, split or otherwise behave in an erratic manner. Finally, the close dimensional tolerances that must be maintained at the gaps makes the propagation of the permalloy overlays more difficult and increases the likelihood of serious propagation errors occurring at the gaps.
Several propagation structures which are generally of a gapless form have been proposed in the prior art, as typified by U.S. Pat. No. 3,516,077 (tangent discs on alternately opposite sides of a platelet), U.S. Pat. No. 3,518,643 (zig-zag strip), and U.S. Pat. No. 3,644,908 (sinuous magnetically hard strip alongside a straight strip). All of these structures have a number of disadvantages, however, such as low packing density and the ability to implement bubble domain movement in only a single direction.
Accordingly, it is a primary object of this invention to provide an improved bubble domain propagation structure which can be used to provide high density storage.
It is another object of this invention to provide magnetic bubble domain propagation by a high density structure which is easily fabricated.
It is a further object of this invention to provide an improved gapless propagation structure for movement of magnetic bubble domains in a supporting magnetic medium.